The role of escaped farmed salmon in spreading infectious agents from aquaculture to wild salmonid populations is largely unknown. This is a case study of potential disease interaction between escaped farmed and wild fish populations. In summer 2012, significant numbers of farmed Atlantic salmon were captured in the Hardangerfjord and in a local river. Genetic analyses of 59 of the escaped salmon and samples collected from six local salmon farms pointed out the most likely source farm, but two other farms had an overlapping genetic profile. The escapees were also analysed for three viruses that are prevalent in fish farming in Norway. Almost all the escaped salmon were infected with salmon alphavirus (SAV) and piscine reovirus (PRV). To use the infection profile to assist genetic methods in identifying the likely farm of origin, samples from the farms were also tested for these viruses. However, in the current case, all the three farms had an infection profile that was similar to that of the escapees. We have shown that double-virus-infected escaped salmon ascend a river close to the likely source farms, reinforcing the potential for spread of viruses to wild salmonids.

Heart and skeletal muscle inflammation (HSMI) caused by piscine orthoreovirus (PRV) and pancreas disease (PD) caused by salmonid alphavirus (SAV) are among the most prevalent viral diseases of Atlantic salmon farmed in Norway. There are limited data about the impact of disease in farmed salmon on wild salmon populations. Therefore, the prevalence of PRV and SAV in returning salmon caught in six sea sites was determined using real-time RT-PCR analyses. Of 419 salmon tested, 15.8% tested positive for PRV, while none were positive for SAV. However, scale reading revealed that 10% of the salmon had escaped from farms. The prevalence of PRV in wild salmon (8%) was significantly lower than in farm escapees (86%), and increased with fish length (proxy for age). Sequencing of the S1 gene of PRV from 39 infected fish revealed a mix of genotypes. The observed increase in PRV prevalence with fish age and the lack of phylogeographic structure of the virus could be explained by virus transmission in the feeding areas. Our results highlight the need for studies about the prevalence of PRV and other pathogens in Atlantic salmon in its oceanic phase. Disease outbreaks in salmon farms may lead to increased infection and disease risks at neighbouring farms and in wild fish populations, and there is an increasing public concern of disease impacting wild salmon populations in Norway (Sv asand et al., 2017). Data are collected annually on the frequency and geographical distribution of disease outbreaks in fish farms (Hjeltnes et al., 2017). Correlating such data from regions differing in farming intensities and disease profiles with pathogen prevalence in local wild salmon populations would thus help to address this concern. However, pathogen prevalence data alone as an indicator of infection pressure have ----------------------------------------------------This is an open access article under the terms of the Creative Commons Attribution License, which permits use, distribution and reproduction in any medium, provided the original work is properly cited.

Viral diseases represent a serious problem in Atlantic salmon (Salmo salar L.) farming in Norway. Pancreas disease (PD) caused by salmonid alphavirus (SAV) and heart and skeletal muscle inflammation (HSMI) caused by piscine orthoreovirus (PRV) are among the most frequently diagnosed viral diseases in recent years. The possible spread of viruses from salmon farms to wild fish is a major public concern. Sea trout S. trutta collected from the major farming areas along the Norwegian coast are likely to have been exposed to SAV and PRV from farms with disease outbreaks. We examined 843 sea trout from 4 counties in Norway for SAV and PRV infections. We did not detect SAV in any of the tested fish, although significant numbers of the trout were caught in areas with frequent PD outbreaks. Low levels of PRV were detected in 1.3% of the sea trout. PRV-infected sea trout were caught in both salmon farming and non-farming areas, so the occurrence of infections was not associated with farming intensity or HSMI cases. Our results suggest that SAV and PRV infections are uncommon in wild sea trout. Hence, we found no evidence that sea trout are at risk from SAV or PRV released from salmon farms.

A total of 30 isolates of Francisella noatunensis subsp. noatunensis isolated from Atlantic cod Gadus morhua L. were tested for susceptibility, in the form of minimal inhibitory concentration (MIC) values, against the following antibacterial agents: flumequine, oxolinic acid, ciprofloxacin, florfenicol, oxytetracycline, erythromycin, streptomycin sulphate, trimetoprim/ sulphadiazine and rifampin. All the isolates had a low susceptibility to oxytetracycline, trimetoprim/sulphadiazine (Tribrissen ® ), erythromycin, ciprofloxacin and streptomycin with MIC values of 64, 64 to 128, 16, 8 and 32 to 128 µg ml Dis Aquat Org 98: [57][58][59][60][61][62] 2012 markedly more active against oxolinic-acid-resistant isolates of Aeromonas salmonicida (Lewin & Hastings 1990). F. noatunensis subsp. noatunensis is a slowgrowing bacterium, and rifampin, erythromycin and streptomycin sulphate are all antibacterial agents that are used in human medicine in the treatment of Mycobacterium tuberculosis, another slow-growing bacterium. Erythromycin is also occasionally used against bacterial kidney disease (BKD) in salmonids.The aim of the present study was to test the susceptibility, in the form of MIC values, to a number of isolates of Francisella noatunensis subsp. noatunensis against the selected group of antibacterial agents. MATERIALS AND METHODS Bacterial strainsA total of 30 isolates of Francisella noatunensis subsp. noatunensis from Atlantic cod Gadus morhua L. were analysed. Of these, 28 isolates were provided by the Norwegian Veterinary Institute (Norway) and 2 isolates, GM2212/LMG 24256 (Nylund et al. 2006, Ottem et al. 2007) and EK-4b, were provided by the Institute of Marine Research (Norway). All isolates originate from farmed cod, except EK-4b, which was isolated from a wild cod. The strains were previously identified as F. noatunensis subsp. noatunensis using the methods described by Ottem et al. (2008). ChemicalsFlumequine, oxolinic acid, oxytetracycline, florfenicol, Tribrissen (trimethoprim/sulfadiazine), erythromycin, ciprofloxacin, streptomycin sulphate and rifampin were all obtained from Norwegian Medical Depot (Bergen, Norway). Stock solutions of antibacterial agents were prepared at a concentration of 1.0 mg ml −1 in methanol (florfenicol, Tribrissen, rifampin), in water (oxytetracycline, erythromycin, streptomycin sulphate), 0.03 M NaOH (flumequine, oxolic acid) and 0.03 M NaOH/methanol (1:1) (ciprofloxacin). MIC determinationIn order to meet the demands of Francisella noatunensis subsp. noatunensis for specific growth factors, the method of choice in the present work was a modified agar dilution test for the determinations of MIC values (Alderman & Smith 2001). Briefly, F. noatunensis subsp. noatunensis isolates were grown on modified Mueller-Hinton agar (MMHA) supplemented with 3% foetal bovine serum (FBS) (PAA Laboratories), 0.8% glucose (Merck), 0.4% L-cystein (Sigma) and 4% Yeastolate Ultrafiltrate (Gibco) and containing 2-fold dilutions of the antibacterial agents tested. All supplements and a...